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Datomic Free → Datomic Pro

Why

Datomic Free 0.9.5703 does not work on Java 21. The peer-to-transactor connection fails with an SSL handshake timeout in ActiveMQ Artemis (Datomic's internal messaging layer). This is not configurable — Datomic Free is unmaintained and will never be fixed.

Datomic Pro is free under the Apache 2.0 license and supports Java 11, 17, and 21.

What Changed

Connection URI

# Before (Datomic Free)
datomic:free://localhost:4334/orcpub

# After (Datomic Pro dev protocol)
datomic:dev://localhost:4334/orcpub

The dev protocol uses the Datomic Pro dev transactor (same data model, same API, different transport).

Maven Dependency

;; Before
[com.datomic/datomic-free "0.9.5703"]

;; After
[com.datomic/peer "1.0.7482" :exclusions [org.slf4j/slf4j-nop]]

The Datomic Pro peer library is com.datomic/peer (not com.datomic/datomic-pro). The slf4j-nop exclusion avoids duplicate SLF4J binding warnings.

Installation

Datomic Pro is installed during container creation by .devcontainer/post-create.sh:

  1. Downloads the Datomic Pro zip from S3
  2. Extracts to lib/com/datomic/datomic-pro/<version>/
  3. Runs bin/maven-install to populate the local Maven repository

The peer JAR resolves via the existing file:lib repository pattern in project.clj.

Transactor

The transactor is a separate process started by scripts/start.sh datomic. It uses a properties file generated from the template at the Datomic install path. The transactor is not a JAR — it's the bin/transactor script with a config file.

Configuration

All Datomic config flows through src/clj/orcpub/config.clj:

(config/get-datomic-uri)
;; Returns DATOMIC_URL env var or default "datomic:dev://localhost:4334/orcpub"

Environment variables (see .env.example):

  • DATOMIC_URL — connection URI
  • DATOMIC_VERSION — version for installer (default: 1.0.7482)
  • DATOMIC_TYPE — pro (default)
  • DATOMIC_PASSWORD — transactor password

Code Changes

File Change
project.clj datomic-free → com.datomic/peer, version 1.0.7482
src/clj/orcpub/config.clj New — get-datomic-uri, datomic-env (SSOT for URI)
src/clj/orcpub/system.clj Uses config/get-datomic-uri instead of inline logic
src/clj/orcpub/datomic.clj Connection logic unchanged — datomic.api is the same
dev/user.clj init-database uses config/datomic-env
.devcontainer/post-create.sh Datomic Pro installer (download, extract, maven-install)
.env.example Datomic Pro defaults

Datomock Compatibility

The test suite uses datomock for in-memory database testing. The original vvvvalvalval/datomock 0.2.0 causes AbstractMethodError with Datomic Pro (new transact signature). Replaced with org.clojars.favila/datomock 0.2.2-favila1.